draft-ietf-uta-smtp-tlsrpt-23.txt   rfc8460.txt 
Using TLS in Applications D. Margolis Internet Engineering Task Force (IETF) D. Margolis
Internet-Draft Google, Inc Request for Comments: 8460 Google, Inc.
Intended status: Standards Track A. Brotman Category: Standards Track A. Brotman
Expires: December 16, 2018 Comcast, Inc ISSN: 2070-1721 Comcast, Inc.
B. Ramakrishnan B. Ramakrishnan
Yahoo!, Inc Oath, Inc.
J. Jones J. Jones
Microsoft, Inc Microsoft, Inc.
M. Risher M. Risher
Google, Inc Google, Inc.
June 14, 2018 September 2018
SMTP TLS Reporting SMTP TLS Reporting
draft-ietf-uta-smtp-tlsrpt-23
Abstract Abstract
A number of protocols exist for establishing encrypted channels A number of protocols exist for establishing encrypted channels
between SMTP Mail Transfer Agents, including STARTTLS, DANE TLSA, and between SMTP Mail Transfer Agents (MTAs), including STARTTLS, DNS-
MTA-STS. These protocols can fail due to misconfiguration or active Based Authentication of Named Entities (DANE) TLSA, and MTA Strict
attack, leading to undelivered messages or delivery over unencrypted Transport Security (MTA-STS). These protocols can fail due to
or unauthenticated channels. This document describes a reporting misconfiguration or active attack, leading to undelivered messages or
mechanism and format by which sending systems can share statistics delivery over unencrypted or unauthenticated channels. This document
and specific information about potential failures with recipient describes a reporting mechanism and format by which sending systems
domains. Recipient domains can then use this information to both can share statistics and specific information about potential
detect potential attacks and diagnose unintentional failures with recipient domains. Recipient domains can then use this
misconfigurations. information to both detect potential attacks and diagnose
unintentional misconfigurations.
Status of This Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This is an Internet Standards Track document.
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months This document is a product of the Internet Engineering Task Force
and may be updated, replaced, or obsoleted by other documents at any (IETF). It represents the consensus of the IETF community. It has
time. It is inappropriate to use Internet-Drafts as reference received public review and has been approved for publication by the
material or to cite them other than as "work in progress." Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 7841.
This Internet-Draft will expire on December 16, 2018. Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
https://www.rfc-editor.org/info/rfc8460.
Copyright Notice Copyright Notice
Copyright (c) 2018 IETF Trust and the persons identified as the Copyright (c) 2018 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of (https://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License. described in the Simplified BSD License.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 4 1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 4
2. Related Technologies . . . . . . . . . . . . . . . . . . . . 4 2. Related Technologies . . . . . . . . . . . . . . . . . . . . 5
3. Reporting Policy . . . . . . . . . . . . . . . . . . . . . . 5 3. Reporting Policy . . . . . . . . . . . . . . . . . . . . . . 6
3.1. Example Reporting Policy . . . . . . . . . . . . . . . . 7 3.1. Example Reporting Policy . . . . . . . . . . . . . . . . 8
3.1.1. Report using MAILTO . . . . . . . . . . . . . . . . . 7 3.1.1. Report Using MAILTO . . . . . . . . . . . . . . . . . 8
3.1.2. Report using HTTPS . . . . . . . . . . . . . . . . . 7 3.1.2. Report Using HTTPS . . . . . . . . . . . . . . . . . 8
4. Reporting Schema . . . . . . . . . . . . . . . . . . . . . . 7 4. Reporting Schema . . . . . . . . . . . . . . . . . . . . . . 8
4.1. Report Time-frame . . . . . . . . . . . . . . . . . . . . 8 4.1. Report Time Frame . . . . . . . . . . . . . . . . . . . . 9
4.2. Delivery Summary . . . . . . . . . . . . . . . . . . . . 9 4.2. Delivery Summary . . . . . . . . . . . . . . . . . . . . 10
4.2.1. Success Count . . . . . . . . . . . . . . . . . . . . 9 4.2.1. Success Count . . . . . . . . . . . . . . . . . . . . 10
4.2.2. Failure Count . . . . . . . . . . . . . . . . . . . . 9 4.2.2. Failure Count . . . . . . . . . . . . . . . . . . . . 10
4.3. Result Types . . . . . . . . . . . . . . . . . . . . . . 9 4.3. Result Types . . . . . . . . . . . . . . . . . . . . . . 10
4.3.1. Negotiation Failures . . . . . . . . . . . . . . . . 10 4.3.1. Negotiation Failures . . . . . . . . . . . . . . . . 10
4.3.2. Policy Failures . . . . . . . . . . . . . . . . . . . 10 4.3.2. Policy Failures . . . . . . . . . . . . . . . . . . . 11
4.3.3. General Failures . . . . . . . . . . . . . . . . . . 11 4.3.3. General Failures . . . . . . . . . . . . . . . . . . 11
4.3.4. Transient Failures . . . . . . . . . . . . . . . . . 11 4.3.4. Transient Failures . . . . . . . . . . . . . . . . . 12
4.4. JSON Report Schema . . . . . . . . . . . . . . . . . . . 11 4.4. JSON Report Schema . . . . . . . . . . . . . . . . . . . 12
4.5. Policy Samples . . . . . . . . . . . . . . . . . . . . . 14 4.5. Policy Samples . . . . . . . . . . . . . . . . . . . . . 15
5. Report Delivery . . . . . . . . . . . . . . . . . . . . . . . 15 5. Report Delivery . . . . . . . . . . . . . . . . . . . . . . . 15
5.1. Report Filename . . . . . . . . . . . . . . . . . . . . . 15 5.1. Report Filename . . . . . . . . . . . . . . . . . . . . . 16
5.2. Compression . . . . . . . . . . . . . . . . . . . . . . . 16 5.2. Compression . . . . . . . . . . . . . . . . . . . . . . . 17
5.3. Email Transport . . . . . . . . . . . . . . . . . . . . . 16 5.3. Email Transport . . . . . . . . . . . . . . . . . . . . . 17
5.3.1. Example Report . . . . . . . . . . . . . . . . . . . 17 5.3.1. Example Report . . . . . . . . . . . . . . . . . . . 19
5.4. HTTPS Transport . . . . . . . . . . . . . . . . . . . . . 18 5.4. HTTPS Transport . . . . . . . . . . . . . . . . . . . . . 19
5.5. Delivery Retry . . . . . . . . . . . . . . . . . . . . . 19 5.5. Delivery Retry . . . . . . . . . . . . . . . . . . . . . 20
5.6. Metadata Variances . . . . . . . . . . . . . . . . . . . 19 5.6. Metadata Variances . . . . . . . . . . . . . . . . . . . 20
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 19 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 20
6.1. Message headers . . . . . . . . . . . . . . . . . . . . . 19 6.1. Message Headers . . . . . . . . . . . . . . . . . . . . . 20
6.2. Report Type . . . . . . . . . . . . . . . . . . . . . . . 19 6.2. Report Type . . . . . . . . . . . . . . . . . . . . . . . 21
6.3. +gzip Media Type Suffix . . . . . . . . . . . . . . . . . 20 6.3. +gzip Media Type Suffix . . . . . . . . . . . . . . . . . 22
6.4. application/tlsrpt+json Media Type . . . . . . . . . . . 21 6.4. application/tlsrpt+json Media Type . . . . . . . . . . . 23
6.5. application/tlsrpt+gzip Media Type . . . . . . . . . . . 23 6.5. application/tlsrpt+gzip Media Type . . . . . . . . . . . 24
6.6. STARTTLS Validation Result Types . . . . . . . . . . . . 24 6.6. STARTTLS Validation Result Types . . . . . . . . . . . . 25
7. Security Considerations . . . . . . . . . . . . . . . . . . . 24 7. Security Considerations . . . . . . . . . . . . . . . . . . . 26
8. Privacy Considerations . . . . . . . . . . . . . . . . . . . 26 8. Privacy Considerations . . . . . . . . . . . . . . . . . . . 27
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 26 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 28
9.1. Normative References . . . . . . . . . . . . . . . . . . 26 9.1. Normative References . . . . . . . . . . . . . . . . . . 28
9.2. Informative References . . . . . . . . . . . . . . . . . 28 9.2. Informative References . . . . . . . . . . . . . . . . . 30
9.3. URIs . . . . . . . . . . . . . . . . . . . . . . . . . . 29 Appendix A. Example Reporting Policy . . . . . . . . . . . . . . 32
Appendix A. Example Reporting Policy . . . . . . . . . . . . . . 30 A.1. Report Using MAILTO . . . . . . . . . . . . . . . . . . . 32
A.1. Report using MAILTO . . . . . . . . . . . . . . . . . . . 30 A.2. Report Using HTTPS . . . . . . . . . . . . . . . . . . . 32
A.2. Report using HTTPS . . . . . . . . . . . . . . . . . . . 30 Appendix B. Example JSON Report . . . . . . . . . . . . . . . . 32
Appendix B. Example JSON Report . . . . . . . . . . . . . . . . 30 Contributors . . . . . . . . . . . . . . . . . . . . . . . . . . 34
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 32 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 34
1. Introduction 1. Introduction
The STARTTLS extension to SMTP [RFC3207] allows SMTP clients and The STARTTLS extension to SMTP [RFC3207] allows SMTP clients and
hosts to establish secure SMTP sessions over TLS. The protocol hosts to establish secure SMTP sessions over TLS. The protocol
design uses an approach that has come to be known as "Opportunistic design uses an approach that has come to be known as "Opportunistic
Security" (OS) [RFC7435]. This method maintains interoperability Security" (OS) [RFC7435]. This method maintains interoperability
with clients that do not support STARTTLS, but means that any with clients that do not support STARTTLS, but it means that any
attacker could potentially eavesdrop on a session. An attacker could attacker could potentially eavesdrop on a session. An attacker could
perform a downgrade or interception attack by deleting parts of the perform a downgrade or interception attack by deleting parts of the
SMTP session (such as the "250 STARTTLS" response) or redirect the SMTP session (such as the "250 STARTTLS" response) or redirect the
entire SMTP session (perhaps by overwriting the resolved MX record of entire SMTP session (perhaps by overwriting the resolved MX record of
the delivery domain). the delivery domain).
Because such "downgrade attacks" are not necessarily apparent to the Because such "downgrade attacks" are not necessarily apparent to the
receiving MTA, this document defines a mechanism for sending domains receiving MTA, this document defines a mechanism for sending domains
to report on failures at multiple stages of the MTA-to-MTA to report on failures at multiple stages of the MTA-to-MTA
conversation. conversation.
Recipient domains may also use the mechanisms defined by MTA-STS Recipient domains may also use the mechanisms defined by MTA-STS
[I-D.ietf-uta-mta-sts] or DANE [RFC6698] to publish additional [RFC8461] or DANE [RFC6698] to publish additional encryption and
encryption and authentication requirements; this document defines a authentication requirements; this document defines a mechanism for
mechanism for sending domains that are compatible with MTA-STS or sending domains that are compatible with MTA-STS or DANE to share
DANE to share success and failure statistics with recipient domains. success and failure statistics with recipient domains.
Specifically, this document defines a reporting schema that covers Specifically, this document defines a reporting schema that covers
failures in routing, DNS resolution, STARTTLS negotiation, and both failures in routing, DNS resolution, and STARTTLS negotiation; policy
DANE [RFC6698] and MTA-STS [I-D.ietf-uta-mta-sts] policy validation validation errors for both DANE [RFC6698] and MTA-STS [RFC8461]; and
errors, and a standard TXT record that recipient domains can use to a standard TXT record that recipient domains can use to indicate
indicate where reports in this format should be sent. The report can where reports in this format should be sent. The report can also
also serve as a heartbeat that systems are successfully negotiating serve as a heartbeat to indicate that systems are successfully
TLS during sessions as expected. negotiating TLS during sessions as expected.
This document is intended as a companion to the specification for This document is intended as a companion to the specification for
SMTP MTA Strict Transport Security [I-D.ietf-uta-mta-sts], as well as SMTP MTA-STS [RFC8461] and adds reporting abilities for those
adds reporting abilities for those implementing DANE [RFC7672]. implementing DANE [RFC7672].
1.1. Terminology 1.1. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in "OPTIONAL" in this document are to be interpreted as described in
[BCP 14] [RFC2119] [RFC8174] when, and only when, they appear in all BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here. capitals, as shown here.
We also define the following terms for further use in this document: We also define the following terms for further use in this document:
o MTA-STS Policy: A mechanism by which administrators can specify o MTA-STS Policy: A mechanism by which administrators can specify
the expected TLS availability, presented identity, and desired the expected TLS availability, presented identity, and desired
actions for a given email recipient domain. MTA-STS is defined in actions for a given email recipient domain. MTA-STS is defined in
[I-D.ietf-uta-mta-sts]. [RFC8461].
o DANE Policy: A mechanism by which administrators can use DNSSEC to o DANE Policy: A mechanism by which administrators can use DNSSEC to
commit an MTA to support STARTTLS and to publish criteria to be commit an MTA to support STARTTLS and to publish criteria to be
used to validate its presented certificates. DANE for SMTP is used to validate its presented certificates. DANE for SMTP is
defined in [RFC7672], with the base specification in [RFC6698] defined in [RFC7672], with the base specification defined in
(updated in [RFC7671]. [RFC6698] (and updated by [RFC7671]).
o TLSRPT Policy: A policy specifying the endpoint to which sending o TLSRPT (TLS Reporting) Policy: A policy specifying the endpoint to
MTAs should deliver reports. which Sending MTAs should deliver reports.
o Policy Domain: The domain against which an MTA-STS or DANE Policy o Policy Domain: The domain against which a TLSRPT, an MTA-STS, or a
is defined. For MTA-STS this is typically the same as the DANE policy is defined. For TLSRPT and MTA-STS, this is typically
envelope recipient domain [RFC5321], but when mail is routed to a the same as the envelope recipient domain [RFC5321], but when mail
"smarthost" gateway by local policy, the "smarthost" domain name is routed to a "smarthost" gateway by local policy, the
is used instead. For DANE the Policy Domain is the "TLSA base "smarthost" domain name is used instead. For DANE, the Policy
domain" of the receiving SMTP server as described in RFC7672 [1] Domain is the "TLSA base domain" of the receiving SMTP server as
and RFC6698 [2]. described in Section 2.2.3 of RFC 7672 and Section 3 of RFC 6698.
o Sending MTA: The MTA initiating the relay of an email message. o Sending MTA: The MTA initiating the relay of an email message.
o Aggregate Report URI (rua): A comma-separated list of locations o Aggregate Report URI (rua): A comma-separated list of locations
where the report is to be submitted. where the report is to be submitted.
o ABNF: Augmented Backus-Naur Form, a syntax for formally specifying
syntax, defined in [RFC5234] and [RFC7405].
2. Related Technologies 2. Related Technologies
o This document is intended as a companion to the specification for o This document is intended as a companion to the specification for
SMTP MTA Strict Transport Security [I-D.ietf-uta-mta-sts]. SMTP MTA-STS [RFC8461].
o SMTP-TLSRPT defines a mechanism for sending domains that are o SMTP TLSRPT defines a mechanism for sending domains that are
compatible with MTA-STS or DANE to share success and failure compatible with MTA-STS or DANE to share success and failure
statistics with recipient domains. DANE is defined in [RFC6698] statistics with recipient domains. DANE is defined in [RFC6698],
and MTA-STS is defined in [I-D.ietf-uta-mta-sts]. and MTA-STS is defined in [RFC8461].
3. Reporting Policy 3. Reporting Policy
A domain publishes a record to its DNS indicating that it wishes to A domain publishes a record to its DNS indicating that it wishes to
receive reports. These SMTP TLSRPT policies are distributed via DNS receive reports. These SMTP TLSRPT policies are distributed via DNS
from the Policy Domain's zone, as TXT records (similar to DMARC from the Policy Domain's zone as TXT records (similar to Domain-based
policies) under the name "_smtp._tls". For example, for the Policy Message Authentication, Reporting, and Conformance (DMARC) policies)
Domain "example.com", the recipient's TLSRPT policy can be retrieved under the name "_smtp._tls". For example, for the Policy Domain
from "_smtp._tls.example.com". "example.com", the recipient's TLSRPT policy can be retrieved from
"_smtp._tls.example.com".
Policies consist of the following directives: Policies consist of the following directives:
o "v": This document defines version 1 of TLSRPT, for which this o "v": This document defines version 1 of TLSRPT, for which this
value MUST be equal to "TLSRPTv1". Other versions may be defined value MUST be equal to "TLSRPTv1". Other versions may be defined
in later documents. in later documents.
o "rua": A URI specifying the endpoint to which aggregate o "rua": A URI specifying the endpoint to which aggregate
information about policy validation results should be sent (see information about policy validation results should be sent (see
Section 4, "Reporting Schema", for more information). Two URI Section 4, "Reporting Schema", for more information). Two URI
schemes are supported: "mailto" and "https". As with DMARC schemes are supported: "mailto" and "https". As with DMARC
[RFC7489], the policy domain can specify a comma-separated list of [RFC7489], the Policy Domain can specify a comma-separated list of
URIs. URIs.
o In the case of "https", reports should be submitted via POST o In the case of "https", reports should be submitted via POST
([RFC7231]) to the specified URI. Report submitters MAY ignore [RFC7231] to the specified URI. Report submitters MAY ignore
certificate validation errors when submitting reports via https. certificate validation errors when submitting reports via HTTPS
POST.
o In the case of "mailto", reports should be submitted to the o In the case of "mailto", reports should be submitted to the
specified email address ([RFC6068]). When sending failure reports specified email address [RFC6068]. When sending failure reports
via SMTP, sending MTAs MUST deliver reports despite any TLS- via SMTP, Sending MTAs MUST deliver reports despite any TLS-
related failures and SHOULD NOT include this SMTP session in the related failures and SHOULD NOT include this SMTP session in the
next report. When sending failure reports via HTTPS, sending MTAs next report. This may mean that the reports are delivered
MAY deliver reports despite any TLS-related faliures. This may unencrypted. Reports sent via SMTP MUST contain a valid
mean that the reports are delivered in the clear. Reports sent DomainKeys Identified Mail (DKIM) [RFC6376] signature by the
via SMTP MUST contain a valid DKIM [RFC6376] signature by the
reporting domain. Reports lacking such a signature MUST be reporting domain. Reports lacking such a signature MUST be
ignored by the recipient. DKIM signatures must not use the "l=" ignored by the recipient. DKIM signatures MUST NOT use the "l="
attribute to limit the body length used in the signature. The attribute to limit the body length used in the signature. This
DKIM TXT record must contain the appropriate service type ensures attackers cannot append extraneous or misleading data to a
declaration, "s=tlsrpt", and if not present the receiving system report without breaking the signature. The DKIM TXT record SHOULD
SHOULD ignore reports signed using this record. contain the appropriate service type declaration, "s=tlsrpt". If
not present, the receiving system MAY ignore reports lacking that
service type.
Sample DKIM record:
dkim_selector._domainkey.example.com TXT
"v=DKIM1;k=rsa;s=tlsrpt;p=Mlf4qwSZfase4fa=="
The formal definition of the "_smtp._tls" TXT record, defined using The formal definition of the "_smtp._tls" TXT record, defined using
[RFC5234] & [RFC7405], is as follows: [RFC5234] and [RFC7405], is as follows:
tlsrpt-record = tlsrpt-version 1*(field-delim tlsrpt-field) tlsrpt-record = tlsrpt-version 1*(field-delim tlsrpt-field)
[field-delim] [field-delim]
field-delim = *WSP ";" *WSP field-delim = *WSP ";" *WSP
tlsrpt-field = tlsrpt-rua / ; Note that the tlsrpt-field = tlsrpt-rua / ; Note that the
tlsrpt-extension ; tlsrpt-rua record is tlsrpt-extension ; tlsrpt-rua record is
; required. ; required.
skipping to change at page 6, line 35 skipping to change at page 7, line 38
tlsrpt-extension = tlsrpt-ext-name "=" tlsrpt-ext-value tlsrpt-extension = tlsrpt-ext-name "=" tlsrpt-ext-value
tlsrpt-ext-name = (ALPHA / DIGIT) *31(ALPHA / tlsrpt-ext-name = (ALPHA / DIGIT) *31(ALPHA /
DIGIT / "_" / "-" / ".") DIGIT / "_" / "-" / ".")
tlsrpt-ext-value = 1*(%x21-3A / %x3C / %x3E-7E) tlsrpt-ext-value = 1*(%x21-3A / %x3C / %x3E-7E)
; chars excluding "=", ";", SP, and control ; chars excluding "=", ";", SP, and control
; chars ; chars
If multiple TXT records for "_smtp._tls" are returned by the If multiple TXT records for "_smtp._tls" are returned by the
resolver, records which do not begin with "v=TLSRPTv1;" are resolver, records that do not begin with "v=TLSRPTv1;" are discarded.
discarded. If the number of resulting records is not one, senders If the number of resulting records is not one, senders MUST assume
MUST assume the recipient domain does not implement TLSRPT. If the the recipient domain does not implement TLSRPT. If the resulting TXT
resulting TXT record contains multiple strings (as described in record contains multiple strings (as described in Section 3.3 of
Section 3.1.3 of [RFC4408]), then the record MUST be treated as if [RFC7208]), then the record MUST be treated as if those strings are
those strings are concatenated together without adding spaces. concatenated without adding spaces.
The record supports the abillity to declare more than one rua, and if The record supports the ability to declare more than one rua, and if
there exists more than one, the reporter MAY attempt to deliver to there exists more than one, the reporter MAY attempt to deliver to
each of the supported rua destinations. A receiver MAY opt to only each of the supported rua destinations. A receiver MAY opt to only
attempt delivery to one of the endpoints, however the report SHOULD attempt delivery to one of the endpoints; however, the report SHOULD
NOT be considered successfully delivered until one of the endpoints NOT be considered successfully delivered until one of the endpoints
accepts delivery of the report. accepts delivery of the report.
Parsers MUST accept TXT records which are syntactically valid (i.e. Parsers MUST accept TXT records that are syntactically valid (i.e.,
valid key-value pairs separated by semi-colons) and implementing a valid key/value pairs separated by semicolons) and implement a
superset of this specification, in which case unknown fields SHALL be superset of this specification, in which case unknown fields SHALL be
ignored. ignored.
3.1. Example Reporting Policy 3.1. Example Reporting Policy
3.1.1. Report using MAILTO 3.1.1. Report Using MAILTO
_smtp._tls.example.com. IN TXT \ _smtp._tls.example.com. IN TXT \
"v=TLSRPTv1;rua=mailto:reports@example.com" "v=TLSRPTv1;rua=mailto:reports@example.com"
3.1.2. Report using HTTPS 3.1.2. Report Using HTTPS
_smtp._tls.example.com. IN TXT \ _smtp._tls.example.com. IN TXT \
"v=TLSRPTv1; \ "v=TLSRPTv1; \
rua=https://reporting.example.com/v1/tlsrpt" rua=https://reporting.example.com/v1/tlsrpt"
4. Reporting Schema 4. Reporting Schema
The report is composed as a plain text file encoded in the I-JSON The report is composed as a plaintext file encoded in the Internet
format ([RFC7493]). JSON (I-JSON) format [RFC7493].
Aggregate reports contain the following fields: Aggregate reports contain the following fields:
o Report metadata: o Report metadata:
* The organization responsible for the report * The organization responsible for the report
* Contact information for one or more responsible parties for the * Contact information for one or more responsible parties for the
contents of the report contents of the report
* A unique identifier for the report * A unique identifier for the report
* The reporting date range for the report * The reporting date range for the report
o Policy, consisting of: o Policy, consisting of:
* One of the following policy types: (1) The MTA-STS policy * One of the following policy types: (1) the MTA-STS Policy
applied (as a string) (2) The DANE TLSA record applied (as a applied (as a string), (2) the DANE TLSA record applied (as a
string, with each RR entry of the RRset listed and separated by string, with each RR entry of the RRset listed and separated by
a semicolon) (3) The literal string "no-policy-found", if a semicolon), and (3) the literal string "no-policy-found", if
neither a DANE nor MTA-STS policy could be found. neither a DANE nor MTA-STS Policy could be found.
* The domain for which the policy is applied * The domain for which the policy is applied
* The MX host * The MX host
o Aggregate counts, comprising result type, sending MTA IP, o Aggregate counts, comprising result type, Sending MTA IP,
receiving MTA hostname, session count, and an optional additional receiving MTA hostname, session count, and an optional additional
information field containing a URI for recipients to review information field containing a URI for recipients to review
further information on a failure type. further information on a failure type.
Note that the failure types are non-exclusive; an aggregate report Note that the failure types are non-exclusive; an aggregate report
may contain overlapping "counts" of failure types when a single send may contain overlapping "counts" of failure types when a single send
attempt encountered multiple errors. Reporters may report multiple attempt encountered multiple errors. Reporters may report multiple
applied policies (for example, an MTA-STS policy and a DANE TLSA applied policies (for example, an MTA-STS Policy and a DANE TLSA
record for the same domain and MX). Because of this, even in the record for the same domain and MX). Because of this, even in the
case where only a single policy was applied, the "policies" field of case where only a single policy was applied, the "policies" field of
the report body MUST be an array and not a singular value. the report body MUST be an array and not a singular value.
In the case of multiple failure types, the "failure-details" array In the case of multiple failure types, the "failure-details" array
would contain multiple entries. Each entry would have its own set of would contain multiple entries. Each entry would have its own set of
infomation pertaining to that failure type. information pertaining to that failure type.
4.1. Report Time-frame 4.1. Report Time Frame
The report SHOULD cover a full day, from 0000-2400 UTC. This should The report SHOULD cover a full day, from 00:00-24:00 UTC. This
allow for easier correlation of failure events. To avoid a Denial of should allow for easier correlation of failure events. To avoid
Service against the system processing the reports, the reports should unintentionally overloading the system processing the reports, the
be delivered after some delay, perhaps several hours. reports should be delivered after some delay, perhaps several hours.
As an example, a sending site might want to introduce a random delay As an example, a sending site might want to introduce a random delay
of up to four hours: of up to four hours:
func generate_sleep_delay() { func generate_sleep_delay() {
min_delay = 1 min_delay = 1
max_delay = 14400 max_delay = 14400
rand = random(min_delay,max_delay) rand = random(min_delay, max_delay)
return rand return rand
} }
func generate_report(policy_domain) { func generate_report(policy_domain) {
do_rpt_work(policy_domain) do_rpt_work(policy_domain)
send_rpt(policy_domain) send_rpt(policy_domain)
} }
func generate_tlsrpt() { func generate_tlsrpt() {
sleep(generate_sleep_delay()) sleep(generate_sleep_delay())
for policy_domain in list_of_tlsrpt_enabled_domains { for policy_domain in list_of_tlsrpt_enabled_domains {
generate_report(policy_domain) generate_report(policy_domain)
} }
} }
A sending site might wish to introduce a random delay per destination
site, up to four hours:
func generate_sleep_delay() {
min_delay = 1
max_delay = 14400
rand = random(min_delay,max_delay)
return rand
}
func generate_report(policy_domain) {
sleep(generate_sleep_delay())
do_rpt_work(policy_domain)
send_rpt(policy_domain)
}
func generate_tlsrpt() {
for policy_domain in list_of_tlsrpt_enabled_domains {
generate_report(policy_domain)
}
}
4.2. Delivery Summary 4.2. Delivery Summary
4.2.1. Success Count 4.2.1. Success Count
o "total-successful-session-count": This indicates that the sending o "total-successful-session-count": This indicates that the Sending
MTA was able to successfully negotiate a policy-compliant TLS MTA was able to successfully negotiate a policy-compliant TLS
connection, and serves to provide a "heartbeat" to receiving connection and serves to provide a "heartbeat" to receiving
domains that reporting is functional and tabulating correctly. domains that signifies reporting is functional and tabulating
This field contains an aggregate count of successful connections correctly. This field contains an aggregate count of successful
for the reporting system. connections for the reporting system.
4.2.2. Failure Count 4.2.2. Failure Count
o "total-failure-session-count": This indicates that the sending MTA o "total-failure-session-count": This indicates that the Sending MTA
was unable to successfully establish a connection with the was unable to successfully establish a connection with the
receiving platform. Section 4.3, "Result Types", will elaborate receiving platform. Section 4.3, "Result Types", will elaborate
on the failed negotiation attempts. This field contains an on the failed negotiation attempts. This field contains an
aggregate count of failed connections. aggregate count of failed connections.
4.3. Result Types 4.3. Result Types
The list of result types will start with the minimal set below, and The list of result types will start with the minimal set below and is
is expected to grow over time based on real-world experience. The expected to grow over time based on real-world experience. The
initial set is: initial set is outlined in Sections 4.3.1 to 4.3.4:
4.3.1. Negotiation Failures 4.3.1. Negotiation Failures
o "starttls-not-supported": This indicates that the recipient MX did o "starttls-not-supported": This indicates that the recipient MX did
not support STARTTLS. not support STARTTLS.
o "certificate-host-mismatch": This indicates that the certificate o "certificate-host-mismatch": This indicates that the certificate
presented did not adhere to the constraints specified in the MTA- presented did not adhere to the constraints specified in the MTA-
STS or DANE policy, e.g. if the MX hostname does not match any STS or DANE policy, e.g., if the MX hostname does not match any
identities listed in the Subject Alternate Name (SAN) [RFC5280]. identities listed in the subject alternative name (SAN) [RFC5280].
o "certificate-expired": This indicates that the certificate has o "certificate-expired": This indicates that the certificate has
expired. expired.
o "certificate-not-trusted": This a label that covers multiple o "certificate-not-trusted": This is a label that covers multiple
certificate related failures that include, but not limited to certificate-related failures that include, but are not limited to,
errors such as untrusted/unknown CAs, certificate name errors such as untrusted/unknown certification authorities (CAs),
constraints, certificate chain errors etc. When using this certificate name constraints, certificate chain errors, etc. When
declaration, the reporting MTA SHOULD utilize the "failure-reason- using this declaration, the reporting MTA SHOULD utilize the
code" to provide more information to the receiving entity. "failure-reason-code" to provide more information to the receiving
entity.
o "validation-failure": This indicates a general failure for a o "validation-failure": This indicates a general failure for a
reason not matching a category above. When using this reason not matching a category above. When using this
declaration, the reporting MTA SHOULD utilize the "failure-reason- declaration, the reporting MTA SHOULD utilize the "failure-reason-
code" to provide more information to the receiving entity. code" to provide more information to the receiving entity.
4.3.2. Policy Failures 4.3.2. Policy Failures
4.3.2.1. DANE-specific Policy Failures 4.3.2.1. DANE-Specific Policy Failures
o "tlsa-invalid": This indicates a validation error in the TLSA o "tlsa-invalid": This indicates a validation error in the TLSA
record associated with a DANE policy. None of the records in the record associated with a DANE policy. None of the records in the
RRset were found to be valid. RRset were found to be valid.
o "dnssec-invalid": This would indicate that no valid records were o "dnssec-invalid": This indicates that no valid records were
returned from the recursive resolver. The request returned with returned from the recursive resolver.
SERVFAIL for the requested TLSA record.
o "dane-required": This indicates that the sending system is o "dane-required": This indicates that the sending system is
configured to require DANE TLSA records for all the MX hosts of configured to require DANE TLSA records for all the MX hosts of
the destination domain, but no DNSSEC-validated TLSA records were the destination domain, but no DNSSEC-validated TLSA records were
present for the MX host that is the subject of the report. present for the MX host that is the subject of the report.
Mandatory DANE for SMTP is described in section 6 of [RFC7672]. Mandatory DANE for SMTP is described in Section 6 of [RFC7672].
Such policies may be created by mutual agreement between two Such policies may be created by mutual agreement between two
organizations that frequently exchange sensitive content via organizations that frequently exchange sensitive content via
email. email.
4.3.2.2. MTA-STS-specific Policy Failures 4.3.2.2. MTA-STS-specific Policy Failures
o "sts-policy-fetch-error": This indicates a failure to retrieve an
MTA-STS policy, for example, because the policy host is
unreachable.
o "sts-policy-invalid": This indicates a validation error for the o "sts-policy-invalid": This indicates a validation error for the
overall MTA-STS policy. overall MTA-STS Policy.
o "sts-webpki-invalid": This indicates that the MTA-STS policy could o "sts-webpki-invalid": This indicates that the MTA-STS Policy could
not be authenticated using PKIX validation. not be authenticated using PKIX validation.
4.3.3. General Failures 4.3.3. General Failures
When a negotiation failure can not be categorized into one of the When a negotiation failure cannot be categorized into one of the
"Negotiation Failures" stated above, the reporter SHOULD use the "Negotiation Failures" stated above, the reporter SHOULD use the
"validation-failure" category. As TLS grows and becomes more "validation-failure" category. As TLS grows and becomes more
complex, new mechanisms may not be easily categorized. This allows complex, new mechanisms may not be easily categorized. This allows
for a generic feedback category. When this category is used, the for a generic feedback category. When this category is used, the
reporter SHOULD also use the "failure-reason-code" to give some reporter SHOULD also use "failure-reason-code" to give some feedback
feedback to the receiving entity. This is intended to be a short to the receiving entity. This is intended to be a short text field,
text field, and the contents of the field should be an error code or and the contents of the field should be an error code or error text,
error text, such as "X509_V_ERR_UNHANDLED_CRITICAL_CRL_EXTENSION". such as "X509_V_ERR_UNHANDLED_CRITICAL_CRL_EXTENSION".
4.3.4. Transient Failures 4.3.4. Transient Failures
Transient errors due to too-busy network, TCP timeouts, etc. are not Transient errors due to too-busy networks, TCP timeouts, etc., are
required to be reported. not required to be reported.
4.4. JSON Report Schema 4.4. JSON Report Schema
The JSON schema is derived from the HPKP JSON schema [RFC7469] (cf. The JSON schema is derived from the HTTP Public Key Pinning (HPKP)
Section 3) JSON schema; see Section 3 of [RFC7469].
{ {
"organization-name": organization-name, "organization-name": organization-name,
"date-range": { "date-range": {
"start-datetime": date-time, "start-datetime": date-time,
"end-datetime": date-time "end-datetime": date-time
}, },
"contact-info": email-address, "contact-info": email-address,
"report-id": report-id, "report-id": report-id,
"policies": [{ "policies": [{
skipping to change at page 12, line 45 skipping to change at page 13, line 8
] ]
} }
] ]
} }
JSON Report Format JSON Report Format
o "organization-name": The name of the organization responsible for o "organization-name": The name of the organization responsible for
the report. It is provided as a string. the report. It is provided as a string.
o "date-time": The date-time indicates the start- and end-times for o "date-time": The date-time indicates the start and end times for
the report range. It is provided as a string formatted according the report range. It is provided as a string formatted according
to Section 5.6, "Internet Date/Time Format", of [RFC3339]. The to "Internet Date/Time Format", Section 5.6 of [RFC3339]. The
report should be for a full UTC day, 0000-2400. report should be for a full UTC day, 00:00-24:00.
o "email-address": The contact information for a responsible party o "email-address": The contact information for the party responsible
of the report. It is provided as a string formatted according to for the report. It is provided as a string formatted according to
Section 3.4.1, "Addr-Spec", of [RFC5321]. "Addr-Spec Specification", Section 3.4.1 of [RFC5322].
o "report-id": A unique identifier for the report. Report authors o "report-id": A unique identifier for the report. Report authors
may use whatever scheme they prefer to generate a unique may use whatever scheme they prefer to generate a unique
identifier. It is provided as a string. identifier. It is provided as a string.
o "policy-type": The type of policy that was applied by the sending o "policy-type": The type of policy that was applied by the sending
domain. Presently, the only three valid choices are "tlsa", domain. Presently, the only three valid choices are "tlsa",
"sts", and the literal string "no-policy-found". It is provided "sts", and the literal string "no-policy-found". It is provided
as a string. as a string.
o "policy-string": An encoding of the applied policy as a JSON array o "policy-string": An encoding of the applied policy as a JSON array
of strings, whether TLSA record ([RFC6698] section 2.3) or MTA-STS of strings, whether it's a TLSA record ([RFC6698], Section 2.3) or
policy. Examples follow in the next section. an MTA-STS Policy. Examples follow in the next section.
o "domain": The Policy Domain is the domain against which the MTA- o "domain": The Policy Domain against which the MTA-STS or DANE
STS or DANE policy is defined. In the case of Internationalized policy is defined. In the case of Internationalized Domain Names
Domain Names ([RFC5891]), the domain MUST consist of the Punycode- [RFC5891], the domain MUST consist of the Punycode-encoded
encoded A-labels ([RFC3492]) and not the U-labels. A-labels [RFC3492] and not the U-labels.
o "mx-host-pattern": The pattern of MX hostnames from the applied o "mx-host-pattern": In the case where "policy-type" is "sts", it's
policy. It is provided as a string, and is interpreted in the the pattern of MX hostnames from the applied policy. It is
same manner as the "Checking of Wildcard Certificates" rules in provided as a JSON array of strings and is interpreted in the same
Section 6.4.3 of [RFC6125]. In the case of Internationalized manner as the rules in "MX Host Validation"; see Section 4.1 of
Domain Names ([RFC5891]), the domain MUST consist of the Punycode- [RFC8461]. In the case of Internationalized Domain Names
encoded A-labels ([RFC3492]) and not the U-labels. [RFC5891], the domain MUST consist of the Punycode-encoded
A-labels [RFC3492] and not the U-labels.
o "result-type": A value from Section 4.3, "Result Types", above. o "result-type": A value from Section 4.3, "Result Types", above.
o "ip-address": The IP address of the sending MTA that attempted the o "ip-address": The IP address of the Sending MTA that attempted the
STARTTLS connection. It is provided as a string representation of STARTTLS connection. It is provided as a string representation of
an IPv4 (see below) or IPv6 ([RFC5952]) address in dot-decimal or an IPv4 (see below) or IPv6 [RFC5952] address in dot-decimal or
colon-hexadecimal notation. colon-hexadecimal notation.
o "receiving-mx-hostname": The hostname of the receiving MTA MX o "receiving-mx-hostname": The hostname of the receiving MTA MX
record with which the sending MTA attempted to negotiate a record with which the Sending MTA attempted to negotiate a
STARTTLS connection. STARTTLS connection.
o "receiving-mx-helo": (optional) The HELO or EHLO string from the o "receiving-mx-helo" (optional): The HELLO (HELO) or Extended HELLO
banner announced during the reported session. (EHLO) string from the banner announced during the reported
session.
o "receiving-ip": The destination IP address that was using when o "receiving-ip": The destination IP address that was used when
creating the outbound session. It is provided as a string creating the outbound session. It is provided as a string
representation of an IPv4 (see below) or IPv6 ([RFC5952]) address representation of an IPv4 (see below) or IPv6 [RFC5952] address in
in dot-decimal or colon-hexadecimal notation. dot-decimal or colon-hexadecimal notation.
o "total-successful-session-count": The aggregate count (integer, o "total-successful-session-count": The aggregate count (an integer,
encoded as a JSON number) of successfully negotiated TLS-enabled encoded as a JSON number) of successfully negotiated TLS-enabled
connections to the receiving site. connections to the receiving site.
o "total-failure-session-count": The aggregate count (integer, o "total-failure-session-count": The aggregate count (an integer,
encoded as a JSON number) of failures to negotiate a TLS-enabled encoded as a JSON number) of failures to negotiate a TLS-enabled
connection to the receiving site. connection to the receiving site.
o "failed-session-count": The number of (attempted) sessions that o "failed-session-count": The number of (attempted) sessions that
match the relevant "result-type" for this section (integer, match the relevant "result-type" for this section (an integer,
encoded as a JSON number). encoded as a JSON number).
o "additional-info-uri": An optional URI [RFC3986] pointing to o "additional-info-uri" (optional): A URI [RFC3986] that points to
additional information around the relevant "result-type". For additional information around the relevant "result-type". For
example, this URI might host the complete certificate chain example, this URI might host the complete certificate chain
presented during an attempted STARTTLS session. presented during an attempted STARTTLS session.
o "failure-reason-code": A text field to include a TLS-related error o "failure-reason-code": A text field to include a TLS-related error
code or error message. code or error message.
For report purposes, an IPv4 Address is defined via the following For report purposes, an IPv4 address is defined via the following
ABNF: ABNF:
IPv4address = dec-octet "." dec-octet "." dec-octet "." dec-octet IPv4address = dec-octet "." dec-octet "." dec-octet "." dec-octet
dec-octet = DIGIT ; 0-9 dec-octet = DIGIT ; 0-9
/ %x31-39 DIGIT ; 10-99 / %x31-39 DIGIT ; 10-99
/ "1" 2DIGIT ; 100-199 / "1" 2DIGIT ; 100-199
/ "2" %x30-34 DIGIT ; 200-249 / "2" %x30-34 DIGIT ; 200-249
/ "25" %x30-35 ; 250-255 / "25" %x30-35 ; 250-255
And an IPv6 address is defined via the following ABNF:
IPv6address = <as defined in [RFC5954]>
4.5. Policy Samples 4.5. Policy Samples
Part of the report body includes the policy that is applied when Part of the report body includes the policy that is applied when
attemping relay to the destination. attempting relay to the destination.
For DANE TLSA policies, this is a JSON array of strings each For DANE TLSA policies, this is a JSON array of strings each
representing the RDATA of a single TLSA resource record as a space- representing the RDATA of a single TLSA resource record as a space-
separated list of its four TLSA fields; the fields are in separated list of its four TLSA fields; the fields are in
presentation format (defined in [RFC6698] Section 2.2) with no presentation format (defined in [RFC6698], Section 2.2) with no
internal spaces or grouping parentheses: internal spaces or grouping parentheses:
[ [
"3 0 1 1F850A337E6DB9C609C522D136A475638CC43E1ED424F8EEC8513D747D1D085D", "3 0 1 1F850A337E6DB9C609C522D136A475638CC43E1ED424F8EEC8513
"3 0 1 12350A337E6DB9C6123522D136A475638CC43E1ED424F8EEC8513D747D1D1234" D747D1D085D",
] "3 0 1 12350A337E6DB9C6123522D136A475638CC43E1ED424F8EEC8513
D747D1D1234"
]
For MTA-STS policies, this is an array of JSON strings that For MTA-STS policies, this is an array of JSON strings that
represents the policy that is declared by the receiving site, represents the policy that is declared by the receiving site,
including any errors that may be present. Note that where there are including any errors that may be present. Note that where there are
multiple "mx" values, they must be listed as separate "mx" elements multiple "mx" values, they must be listed as separate "mx" elements
in the policy array, rather as a single nested "mx" sub-array. in the policy array rather than as a single nested "mx" sub-array.
[ [
"version: STSv1", "version: STSv1",
"mode: testing", "mode: testing",
"mx: mx1.example.com", "mx: mx1.example.com",
"mx: mx2.example.com", "mx: mx2.example.com",
"mx: mx.backup-example.com", "mx: mx.backup-example.com",
"max_age: 604800" "max_age: 604800"
] ]
5. Report Delivery 5. Report Delivery
Reports can be delivered either as an email message via SMTP or via Reports can be delivered either via SMTP (as an email message) or via
HTTP POST. HTTP POST.
5.1. Report Filename 5.1. Report Filename
The filename is RECOMMENDED to be constructed using the following The filename is RECOMMENDED to be constructed using the following
ABNF: ABNF:
filename = sender "!" policy-domain "!" begin-timestamp filename = sender "!" policy-domain "!" begin-timestamp
"!" end-timestamp [ "!" unique-id ] "." extension "!" end-timestamp [ "!" unique-id ] "." extension
unique-id = 1*(ALPHA / DIGIT) unique-id = 1*(ALPHA / DIGIT)
sender = domain ; From the [RFC5321] that is used sender = domain ; from [RFC5321] -- this is used
; as the domain for the `contact-info` ; as the domain for the `contact-info`
; address in the report body ; address in the report body.
; In the case of Internationalized Domain
; Names [RFC5891], the domain MUST consist of
; the Punycode-encoded A-labels [RFC3492] and
; not the U-labels.
policy-domain = domain policy-domain = domain
; In the case of Internationalized Domain
; Names [RFC5891], the domain MUST consist of
; the Punycode-encoded A-labels [RFC3492] and
; not the U-labels.
begin-timestamp = 1*DIGIT begin-timestamp = 1*DIGIT
; seconds since 00:00:00 UTC January 1, 1970 ; seconds since 00:00:00 UTC January 1, 1970
; indicating start of the time range contained ; indicating start of the time range contained
; in the report ; in the report
end-timestamp = 1*DIGIT end-timestamp = 1*DIGIT
; seconds since 00:00:00 UTC January 1, 1970 ; seconds since 00:00:00 UTC January 1, 1970
; indicating end of the time range contained ; indicating end of the time range contained
; in the report ; in the report
extension = "json" / "json.gz" extension = "json" / "json.gz"
The extension MUST be "json" for a plain JSON file, or "json.gz" for The extension MUST be "json" for a plain JSON file or "json.gz" for a
a JSON file compressed using GZIP. JSON file compressed using gzip.
"unique-id" allows an optional unique ID generated by the Sending MTA "unique-id" allows an optional unique ID generated by the Sending MTA
to distinguish among multiple reports generated simultaneously by to distinguish among multiple reports generated simultaneously by
different sources within the same Policy Domain. For example, this different sources for the same Policy Domain. For example, this is a
is a possible filename for a compressed report to the Policy Domain possible filename for a compressed report to the Policy Domain
"example.net" from the Sending MTA "mail.sndr.example.com": "example.net" from the Sending MTA "mail.sndr.example.com":
"mail.sndr.example.com!example.net!1470013207!1470186007!001.json.gz" "mail.sndr.example.com!example.net!1470013207!1470186007!001.json.gz"
5.2. Compression 5.2. Compression
The report SHOULD be subjected to GZIP [RFC1952] compression for both The report SHOULD be subjected to gzip [RFC1952] compression for both
email and HTTPS transport. Declining to apply compression can cause email and HTTPS transport. Declining to apply compression can cause
the report to be too large for a receiver to process (a commonly the report to be too large for a receiver to process (a commonly
observed receiver limit is ten megabytes); compressing the file observed receiver limit is ten megabytes); compressing the file
increases the chances of acceptance of the report at some compute increases the chances of acceptance of the report at some
cost. computational cost.
5.3. Email Transport 5.3. Email Transport
The report MAY be delivered by email. To make the reports machine- The report MAY be delivered by email. To make the reports machine-
parsable for the receivers, we define a top-level media type parsable for the receivers, we define a top-level media type
"multipart/report" with a new parameter "report-type="tlsrpt"". "multipart/report" with a new parameter "report-type="tlsrpt"".
Inside it, there are two parts: The first part is human readable, Inside it, there are two parts: The first part is human readable,
typically "text/plain", and the second part is machine readable with typically "text/plain", and the second part is machine readable with
a new media type defined called "application/tlsrpt+json". If a new media type defined called "application/tlsrpt+json". If
compressed, the report should use the media type "application/ compressed, the report should use the media type "application/
tlsrpt+gzip". tlsrpt+gzip".
In addition, the following two new top level message header fields In addition, the following two new top-level message header fields
are defined: are defined:
"TLS-Report-Domain: Receiver-Domain" "TLS-Report-Domain: Receiver-Domain"
"TLS-Report-Submitter: Sender-Domain" "TLS-Report-Submitter: Sender-Domain"
The "TLS-Report-Submitter" value MUST match the value found in the The "TLS-Report-Submitter" value MUST match the value found in the
[RFC5321] domain from the "contact-info" from the report body. These domain [RFC5321] of the "contact-info" from the report body. These
message headers MUST be included and should allow for easy searching message header fields MUST be included and should allow for easy
for all reports submitted by a report domain or a particular searching for all reports submitted by a reporting domain or a
submitter, for example in IMAP [RFC3501]: particular submitter, for example, in IMAP [RFC3501]:
"s SEARCH HEADER "TLS-Report-Domain" "example.com"" "s SEARCH HEADER "TLS-Report-Domain" "example.com""
It is presumed that the aggregate reporting address will be equipped It is presumed that the aggregate reporting address will be equipped
to process new message header fields and extract MIME parts with the to process new message header fields and extract MIME parts with the
prescribed media type and filename, and ignore the rest. These prescribed media type and filename, and ignore the rest. These
additional headers SHOULD be included in the DKIM [RFC6376] signature additional headers SHOULD be included in the DKIM [RFC6376] signature
for the message. for the message.
The [RFC5322].Subject field for report submissions SHOULD conform to The RFC5322.Subject field for report submissions SHOULD conform to
the following ABNF: the following ABNF:
tlsrpt-subject = %s"Report" FWS ; "Report" tlsrpt-subject = %s"Report" FWS ; "Report"
%s"Domain:" FWS ; "Domain:" %s"Domain:" FWS ; "Domain:"
domain-name FWS ; per [RFC6376] domain-name FWS ; per [RFC6376]
%s"Submitter:" FWS ; "Submitter:" %s"Submitter:" FWS ; "Submitter:"
domain-name FWS ; per [RFC6376] domain-name FWS ; per [RFC6376]
%s"Report-ID:" FWS ; "Report-ID: %s"Report-ID:" FWS ; "Report-ID:
"<" id-left "@" id-right ">" ; per [RFC5322] "<" id-left "@" id-right ">" ; per [RFC5322]
[CFWS] ; per [RFC5322] [CFWS] ; per [RFC5322]
; (as with FWS) ; (as with FWS)
The first domain-name indicates the DNS domain name about which the The first domain-name indicates the DNS domain name about which the
report was generated. The second domain-name indicates the DNS report was generated. The second domain-name indicates the DNS
domain name representing the Sending MTA generating the report. The domain name representing the Sending MTA generating the report. The
purpose of the Report-ID: portion of the field is to enable the purpose of the "Report-ID:" portion of the field is to enable the
Policy Domain to identify and ignore duplicate reports that might be Policy Domain to identify and ignore duplicate reports that might be
sent by a Sending MTA. sent by a Sending MTA.
For instance, this is a possible Subject field for a report to the For instance, this is a possible Subject field for a report to the
Policy Domain "example.net" from the Sending MTA Policy Domain "example.net" from the Sending MTA
"mail.sender.example.com". It is line-wrapped as allowed by "mail.sender.example.com". It is line-wrapped as allowed by
[RFC5322]: [RFC5322]:
Subject: Report Domain: example.net Subject: Report Domain: example.net
Submitter: mail.sender.example.com Submitter: mail.sender.example.com
skipping to change at page 18, line 37 skipping to change at page 19, line 40
Content-Transfer-Encoding: base64 Content-Transfer-Encoding: base64
Content-Disposition: attachment; Content-Disposition: attachment;
filename="mail.sender.example!example.com! filename="mail.sender.example!example.com!
1013662812!1013749130.json.gz" 1013662812!1013749130.json.gz"
<gzipped content of report> <gzipped content of report>
------=_NextPart_000_024E_01CC9B0A.AFE54C00-- ------=_NextPart_000_024E_01CC9B0A.AFE54C00--
... ...
Note that, when sending failure reports via SMTP, sending MTAs MUST Note that, when sending failure reports via SMTP, Sending MTAs MUST
NOT honor MTA-STS or DANE TLSA failures. NOT honor MTA-STS or DANE TLSA failures.
5.4. HTTPS Transport 5.4. HTTPS Transport
The report MAY be delivered by POST to HTTPS. If compressed, the The report MAY be delivered by POST to HTTPS. If compressed, the
report SHOULD use the media type "application/tlsrpt+gzip", and report SHOULD use the media type "application/tlsrpt+gzip"; otherwise
"application/tlsrpt+json" otherwise (see section Section 6, "IANA it SHOULD use the media type "application/tlsrpt+json" (see
Considerations"). Section 6, "IANA Considerations").
The receiving system MUST return a "successful" response from its The receiving system MUST return a "successful" response from its
HTTPS server, typically a 200 or 201 HTTP code [RFC7321]. Other HTTPS server, typically a 200 or 201 HTTP code [RFC7231]. Other
codes could indicate a delivery failure, and may be retried as per codes could indicate a delivery failure and may be retried as per
local sender policy. The receiving system is not expected to process local sender policy. The receiving system is not expected to process
reports at receipt time, and MAY store them for processing at a later reports at receipt time and MAY store them for processing at a later
time. time.
5.5. Delivery Retry 5.5. Delivery Retry
In the event of a delivery failure, regardless of the delivery In the event of a delivery failure, regardless of the delivery
method, a sender SHOULD attempt redelivery for up to 24hrs after the method, a sender SHOULD attempt redelivery for up to 24 hours after
initial attempt. As previously stated the reports are optional, so the initial attempt. As previously stated, the reports are optional,
while it is ideal to attempt redelivery, it is not required. If so while it is ideal to attempt redelivery, it is not required. If
multiple retries are attempted, ideally they SHOULD be done with multiple retries are attempted, ideally they SHOULD be done with
exponential backoff. exponential backoff.
5.6. Metadata Variances 5.6. Metadata Variances
As stated above, there are a variable number of ways to declare As stated above, there are a variable number of ways to declare
information about the data therein. If any of items declared via information about the data therein. If any of the items declared via
subject or filename disagree with the report, the report MUST be subject or filename disagree with the report, the report MUST be
considered the authoritative source. considered the authoritative source.
6. IANA Considerations 6. IANA Considerations
The following are the IANA considerations discussed in this document. The following are the IANA considerations discussed in this document.
6.1. Message headers 6.1. Message Headers
Below is the Internet Assigned Numbers Authority (IANA) Permanent Below is the Internet Assigned Numbers Authority (IANA) Permanent
Message Header Field registration information per [RFC3864]. Message Header Field registration information per [RFC3864].
Header field name: TLS-Report-Domain Header field name: TLS-Report-Domain
Applicable protocol: mail Applicable protocol: mail
Status: standard Status: standard
Author/Change controller: IETF Author/Change controller: IETF
Specification document(s): this one Specification document(s): RFC 8460
Header field name: TLS-Report-Submitter Header field name: TLS-Report-Submitter
Applicable protocol: mail Applicable protocol: mail
Status: standard Status: standard
Author/Change controller: IETF Author/Change controller: IETF
Specification document(s): this one Specification document(s): RFC 8460
6.2. Report Type 6.2. Report Type
This document creates a new registry for "report-type" parameter to This document creates a new registry for the "report-type" parameter
the Content-Type header field for the "multipart/report" top-level to the Content-Type header field for the "multipart/report" top-level
media type defined in [RFC6522]. media type defined in [RFC6522].
The registry name is "Report Type Registry", and the procedure for The registry name is "Report Type Registry", and the procedure for
updating the registry will be "Specification Required". updating the registry will be "Specification Required" [RFC8126].
An entry in this registry should contain: An entry in this registry should contain:
o the report-type being registered o the report-type being registered
o one or more registered media-types that can be used with this o one or more registered media types that can be used with this
report-type report-type
o the document containing the registration action o the document containing the registration action
o an optional comment o an optional comment
The initial entries are: The initial entries are:
Report-Type: tlsrpt Media Type: application/tlsrpt+gzip, application/ Report-Type: tlsrpt
tlsrpt+json Registered By: [RFCXXXX] Comment: Media types suitable Media Type: application/tlsrpt+gzip, application/tlsrpt+json
for use with this report-type are defined in Sections 6.4 and 6.5 of Registered By: [RFC8460]
[RFCXXXX] Comment: Media types suitable for use with this report-type are
defined in Sections 6.4 and 6.5 of [RFC8460]
Report-Type: disposition-notification Media Type: message/ Report-Type: disposition-notification
disposition-notification Registered By: [RFC8098] Section 10 Media Type: message/disposition-notification
Registered By: [RFC8098], Section 10
Report-Type: disposition-notification Media Type: message/global- Report-Type: disposition-notification
disposition-notification Registered By: [RFC6533] Section 6 Media Type: message/global-disposition-notification
Registered By: [RFC6533], Section 6
Report-Type: delivery-status Media Type: message/delivery-status Report-Type: delivery-status
Registered By: [RFC3464] Appendix D Media Type: message/delivery-status
Registered By: [RFC3464], Section 6.2
Report-Type: delivery-status Media Type: message/global-delivery- Report-Type: delivery-status
status Registered By: [RFC6533] Section 6 Media Type: message/global-delivery-status
Registered By: [RFC6533], Section 6
6.3. +gzip Media Type Suffix 6.3. +gzip Media Type Suffix
This document registers a new media type suffix "+gzip". The GZIP This document registers a new media type suffix "+gzip". The gzip
format is a public domain, cross-platform, interoperable file storage format is a public domain, cross-platform, interoperable file storage
and transfer format, specified in [RFC1952]; it supports compression and transfer format, specified in [RFC1952]; it supports compression
and is used as the underlying representation by a variety of file and is used as the underlying representation by a variety of file
formats. The media type "application/gzip" has been registered for formats. The media type "application/gzip" has been registered for
such files. The suffix "+gzip" MAY be used with any media type whose such files. The suffix "+gzip" MAY be used with any media type whose
representation follows that established for "application/gzip". The representation follows that established for "application/gzip". The
media type structured syntax suffix registration form follows: registration form for the structured syntax suffix for use with media
types is as follows:
Type name: GZIP file storage and transfer format Type name: gzip file storage and transfer format.
+suffix: +gzip +suffix: +gzip
References: [RFC1952][RFC6713]
Encoding considerations: GZIP is a binary encoding. References: [RFC1952] [RFC6713]
Encoding considerations: gzip is a binary encoding.
Fragment identifier considerations: The syntax and semantics of Fragment identifier considerations: The syntax and semantics of
fragment identifiers specified for +gzip SHOULD be as specified for fragment identifiers specified for +gzip SHOULD be as specified for
"application/gzip". (At publication of this document, there is no "application/gzip". (At publication of this document, there is no
fragment identification syntax defined for "application/gzip".) The fragment identification syntax defined for "application/gzip".) The
syntax and semantics for fragment identifiers for a specific "xxx/ syntax and semantics for fragment identifiers for a specific "xxx/
yyy+gzip" SHOULD be processed as follows: yyy+gzip" SHOULD be processed as follows:
For cases defined in +gzip, where the fragment identifier For cases defined in +gzip, where the fragment identifier
resolves per the +gzip rules, then process as specified in resolves per the +gzip rules, process as specified in
+gzip. +gzip.
For cases defined in +gzip, where the fragment identifier does For cases defined in +gzip, where the fragment identifier does
not resolve per the +gzip rules, then process as specified in not resolve per the +gzip rules, process as specified in
"xxx/yyy+gzip". "xxx/yyy+gzip".
For cases not defined in +gzip, then process as specified in For cases not defined in +gzip, process as specified in
"xxx/yyy+gzip". "xxx/yyy+gzip".
Interoperability considerations: n/a Interoperability considerations: N/A
Security considerations: GZIP format doesn't provide confidentiality Security considerations: gzip format doesn't provide confidentiality
protection. Integrity protection is provided by and Adler-32 protection. Integrity protection is provided by an Adler-32
checksum, which is not cryptographically strong. See also security checksum, which is not cryptographically strong. See also the
considerations of [RFC6713]. Each individual media type registered security considerations of [RFC6713]. Each individual media type
with a +gzip suffix can have additional security considerations. registered with a +gzip suffix can have additional security
Additionally, GZIP objects can contain multiple files and associated considerations. Additionally, gzip objects can contain multiple
paths. File paths must be validated when the files are extracted; a files and associated paths. File paths must be validated when the
malicious file path could otherwise cause the extractor to overwrite files are extracted; a malicious file path could otherwise cause the
application or system files. extractor to overwrite application or system files.
Contact: art@ietf.org Contact: art@ietf.org
Author/Change controller: Internet Engineering Task Force Author/Change controller: Internet Engineering Task Force
(mailto:iesg@ietf.org). (iesg@ietf.org).
6.4. application/tlsrpt+json Media Type 6.4. application/tlsrpt+json Media Type
This document registers multiple media types, beginning with Table 1 This document registers multiple media types, beginning with Table 1
below. below.
+-------------+----------------+-------------+-------------------+ +-------------+----------------+-------------+-------------------+
| Type | Subtype | File extn | Specification | | Type | Subtype | File Ext | Specification |
+-------------+----------------+-------------+-------------------+ +-------------+----------------+-------------+-------------------+
| application | tlsrpt+json | .json | Section 5.3 | | application | tlsrpt+json | .json | Section 5.3 |
+-------------+----------------+-------------+-------------------+ +-------------+----------------+-------------+-------------------+
Table 1: SMTP TLS Reporting Media Type Table 1: SMTP TLS Reporting Media Type
Type name: application Type name: application
Subtype name: tlsrpt+json Subtype name: tlsrpt+json
Required parameters: n/a Required parameters: N/A
Optional parameters: n/a Optional parameters: N/A
Encoding considerations: Encoding considerations are identical to Encoding considerations: Encoding considerations are identical to
those specified for the "application/json" media type. See those specified for the "application/json" media type. See
[RFC7493]. [RFC7493].
Security considerations: Security considerations relating to SMTP TLS Security considerations: Security considerations relating to SMTP TLS
Reporting are discussed in Section 7. Reporting are discussed in Section 7.
Interoperability considerations: This document specifies format of Interoperability considerations: This document specifies the format
conforming messages and the interpretation thereof. of conforming messages and the interpretation thereof.
Published specification: Section 5.3 of this document. Published specification: Section 5.3 of RFC 8460.
Applications that use this media type: Mail User Agents (MUA) and Applications that use this media type: Mail User Agents (MUAs) and
Mail Transfer Agents. Mail Transfer Agents.
Additional information: Additional information:
Magic number(s): n/a Deprecated alias names for this type: N/A
File extension(s): ".json" Magic number(s): N/A
Macintosh file type code(s): n/a File extension(s): ".json"
Person & email address to contact for further information: See Macintosh file type code(s): N/A
Authors' Addresses section.
Person & email address to contact for further information:
See the Authors' Addresses section.
Intended usage: COMMON Intended usage: COMMON
Restrictions on usage: n/a Restrictions on usage: N/A
Author: See Authors' Addresses section. Author: See the Authors' Addresses section.
Change controller: Internet Engineering Task Force Change controller: Internet Engineering Task Force (iesg@ietf.org).
(mailto:iesg@ietf.org).
6.5. application/tlsrpt+gzip Media Type 6.5. application/tlsrpt+gzip Media Type
+-------------+----------------+-------------+-------------------+ +-------------+----------------+-------------+-------------------+
| Type | Subtype | File extn | Specification | | Type | Subtype | File Ext | Specification |
+-------------+----------------+-------------+-------------------+ +-------------+----------------+-------------+-------------------+
| application | tlsrpt+gzip | .gz | Section 5.3 | | application | tlsrpt+gzip | .gz | Section 5.3 |
+-------------+----------------+-------------+-------------------+ +-------------+----------------+-------------+-------------------+
Table 2: SMTP TLS Reporting Media Type Table 2: SMTP TLS Reporting Media Type
Type name: application Type name: application
Subtype name: tlsrpt+gzip Subtype name: tlsrpt+gzip
Required parameters: n/a Required parameters: N/A
Optional parameters: n/a Optional parameters: N/A
Encoding considerations: Binary Encoding considerations: Binary
Security considerations: Security considerations relating to SMTP TLS Security considerations: Security considerations relating to SMTP TLS
Reporting are discussed in Section 7. Security considerations Reporting are discussed in Section 7. Security considerations
related to gzip compression are discussed in [RFC6713]. related to gzip compression are discussed in RFC 6713.
Interoperability considerations: This document specifies format of Interoperability considerations: This document specifies the format
conforming messages and the interpretation thereof. of conforming messages and the interpretation thereof.
Published specification: Section 5.3 of this document. Published specification: Section 5.3 of RFC 8460.
Applications that use this media type: Mail User Agents (MUA) and Applications that use this media type: Mail User Agents (MUAs) and
Mail Transfer Agents. Mail Transfer Agents.
Additional information: Additional information:
Magic number(s): The first two bytes are 0x1f, 0x8b. Deprecated alias names for this type: N/A
File extension(s): ".gz" Magic number(s): The first two bytes are 0x1f, 0x8b.
Macintosh file type code(s): n/a File extension(s): ".gz"
Person & email address to contact for further information: See Macintosh file type code(s): N/A
Authors' Addresses section.
Person & email address to contact for further information:
See the Authors' Addresses section.
Intended usage: COMMON Intended usage: COMMON
Restrictions on usage: n/a Restrictions on usage: N/A
Author: See Authors' Addresses section.
Change controller: Internet Engineering Task Force Author: See the Authors' Addresses section.
(mailto:iesg@ietf.org).
Change controller: Internet Engineering Task Force (iesg@ietf.org).
6.6. STARTTLS Validation Result Types 6.6. STARTTLS Validation Result Types
This document creates a new registry, "STARTTLS Validation Result This document creates a new registry, "STARTTLS Validation Result
Types". The initial entries in the registry are: Types". The initial entries in the registry are:
+-------------------------------+-----------+ +-----------------------------+--------------+
| Result Type | Desc | | Result Type | Description |
+-------------------------------+-----------+ +-----------------------------+--------------+
| "starttls-not-supported" | 4.3 | | starttls-not-supported | Section 4.3 |
| "certificate-host-mismatch" | 4.3 | | certificate-host-mismatch | Section 4.3 |
| "certificate-expired" | 4.3 | | certificate-expired | Section 4.3 |
| "tlsa-invalid" | 4.3 | | tlsa-invalid | Section 4.3 |
| "dnssec-invalid" | 4.3 | | dnssec-invalid | Section 4.3 |
| "dane-required" | 4.3 | | dane-required | Section 4.3 |
| "certificate-not-trusted" | 4.3 | | certificate-not-trusted | Section 4.3 |
| "sts-policy-invalid" | 4.3 | | sts-policy-invalid | Section 4.3 |
| "sts-webpki-invalid" | 4.3 | | sts-webpki-invalid | Section 4.3 |
| "validation-failure" | 4.3 | | validation-failure | Section 4.3 |
+-------------------------------+-----------+ | sts-policy-fetch-error | Section 4.3 |
+-----------------------------+--------------+
The above entries are described in section Section 4.3, "Result The above entries are described in Section 4.3, "Result Types". New
Types." New result types can be added to this registry using "Expert result types can be added to this registry using the "Expert Review"
Review" IANA registration policy. IANA registration policy.
7. Security Considerations 7. Security Considerations
SMTP TLS Reporting provides transparency into misconfigurations or SMTP TLS Reporting provides visibility into misconfigurations or
attempts to intercept or tamper with mail between hosts who support attempts to intercept or tamper with mail between hosts who support
STARTTLS. There are several security risks presented by the STARTTLS. There are several security risks presented by the
existence of this reporting channel: existence of this reporting channel:
o Flooding of the Aggregate report URI (rua) endpoint: An attacker o Flooding of the Aggregate Report URI (rua) endpoint: An attacker
could flood the endpoint with excessive reporting traffic and could flood the endpoint with excessive reporting traffic and
prevent the receiving domain from accepting additional reports. prevent the receiving domain from accepting additional reports.
This type of Denial-of-Service attack would limit visibility into This type of Denial-of-Service attack would limit visibility into
STARTTLS failures, leaving the receiving domain blind to an STARTTLS failures, leaving the receiving domain blind to an
ongoing attack. ongoing attack.
o Untrusted content: An attacker could inject malicious code into o Untrusted content: An attacker could inject malicious code into
the report, opening a vulnerability in the receiving domain. the report, exploiting any vulnerabilities in the report-handling
Implementers are advised to take precautions against evaluating systems of the receiving domain. Implementers are advised to take
the contents of the report. precautions against evaluating the contents of the report.
o Report snooping: An attacker could create a bogus TLSRPT record to o Report snooping: An attacker could create a bogus TLSRPT record to
receive statistics about a domain the attacker does not own. receive statistics about a domain the attacker does not own.
Since an attacker able to poison DNS is already able to receive Since an attacker that is able to poison DNS is already able to
counts of SMTP connections (and, absent DANE or MTA-STS policies, receive counts of SMTP connections (and, absent DANE or MTA-STS
actual SMTP message payloads), this does not present a significant policies, actual SMTP message payloads), this does not present a
new vulnerability. significant new vulnerability.
o Ignoring HTTPS validation when submitting reports: When reporting o Ignoring HTTPS validation when submitting reports: When reporting
benign misconfigurations, it is likely that a misconfigured SMTP benign misconfigurations, it is likely that a misconfigured SMTP
server may also mean a misconfigured HTTPS server; as a result, server may also mean a misconfigured HTTPS server; as a result,
reporters who required HTTPS validity on the reporting endpoint reporters who require HTTPS validity on the reporting endpoint may
may fail to alert administrators about such misconfigurations. fail to alert administrators about such misconfigurations.
Conversely, in the event of an actual attack, an attacker who Conversely, in the event of an actual attack, an attacker who
wished to create a gap in reporting and could intercept HTTPS wishes to create a gap in reporting and could intercept HTTPS
reports could, just as easily, simply thwart the resolution of the reports could, just as easily, simply thwart the resolution of the
TLSRPT TXT record or establishment of the TCP session to the HTTPS TLSRPT TXT record or establishment of the TCP session to the HTTPS
endpoint. Furthermore, such a man-in-the-middle attacker could endpoint. Furthermore, such a man-in-the-middle attacker could
discover most or all of the metadata exposed in a report merely discover most or all of the metadata exposed in a report merely
through passive observation. As a result, we consider the risks through passive observation. As a result, we consider the risks
of failure to deliver reports on misconfigurations to outweigh of failure to deliver reports on misconfigurations to outweigh
those of attackers intercepting reports. those of attackers intercepting reports.
o Reports as DDoS: TLSRPT allows specifying destinations for the o Reports as DDoS: TLSRPT allows specifying destinations for the
reports that are outside the authority of the Policy Domain, which reports that are outside the authority of the Policy Domain, which
allows domains to delegate processing of reports to a partner allows domains to delegate processing of reports to a partner
organization. However, an attacker who controls the Policy Domain organization. However, an attacker who controls the Policy Domain
DNS could also use this mechanism to direct the reports to an DNS could also use this mechanism to direct the reports to an
unwitting victim, flooding that victim with excessive reports. unwitting victim, flooding that victim with excessive reports.
DMARC [RFC7489] defines a solution for verifying delegation to DMARC [RFC7489] defines a solution for verifying delegation to
avoid such attacks; the need for this is greater with DMARC, avoid such attacks; the need for this is greater with DMARC,
however, because DMARC allows an attacker to trigger reports to a however, because DMARC allows an attacker to trigger reports to a
target from an innocent third party by sending that third party target from an innocent third party by sending mail to that third
mail (which triggers a report from the third party to the target). party (which triggers a report from the third party to the
In the case of TLSRPT, the attacker would have to induce the third target). In the case of TLSRPT, the attacker would have to induce
party to send the attacker mail in order to trigger reports from the third party to send mail to the attacker in order to trigger
the third party to the victim; this reduces the risk of such an reports from the third party to the victim; this reduces the risk
attack and the need for a verification mechanism. of such an attack and the need for a verification mechanism.
Finally, because TLSRPT is intended to help administrators discover Finally, because TLSRPT is intended to help administrators discover
man-in-the-middle attacks against transport-layer encryption, man-in-the-middle attacks against transport-layer encryption,
including attacks designed to thwart negotiation of encrypted including attacks designed to thwart negotiation of encrypted
connections (by downgrading opportunistic encryption or, in the case connections (by downgrading opportunistic encryption or, in the case
of MTA-STS, preventing discovery of a new MTA-STS policy), we must of MTA-STS, preventing discovery of a new MTA-STS Policy), we must
also consider the risk that an adversary who can induce such a also consider the risk that an adversary who can induce such a
downgrade attack can also prevent discovery of the TLSRPT TXT record downgrade attack can also prevent discovery of the TLSRPT TXT record
(and thus prevent discovery of the successful downgrade attack). (and thus prevent discovery of the successful downgrade attack).
Administrators are thus encouraged to deploy TLSRPT TXT records with Administrators are thus encouraged to deploy TLSRPT TXT records with
a large TTL (reducing the window for successful application of a large TTL (reducing the window for successful application of
transient attacks against DNS resolution of the record) or to deploy transient attacks against DNS resolution of the record) or to deploy
DNSSEC on the deploying zone. DNSSEC on the deploying zone.
8. Privacy Considerations 8. Privacy Considerations
MTAs are generally considered public knowledge, however, the MTAs are generally considered public knowledge; however, the
internals of how those MTAs are configured and the users of those internals of how those MTAs are configured and the users of those
MTAs may not be as public. It should be noted that when providing a MTAs may not be as public. It should be noted that providing a
receiving site with information, it may reveal information about the receiving site with information about TLS failures may reveal
sender's configuration, or even information about the senders information about the sender's configuration or even information
themselves. Consider that by sending a report, it might disclose about the senders themselves. For example, sending a report may
your SSL library version as the inability to negotiate a session may disclose what TLS implementation the sender uses, as the inability to
be a known incompatbility between two library versions, or perhaps negotiate a session may be a known incompatibility between two
commonly used in a operating system release that is centered in a implementations. This may, indirectly, leak information on the
certain region. The risk may be minimal, but should be considered. reporter's operating system or even region, if, for example, a rare
TLS implementation is popular among certain users or in certain
locations.
9. References 9. References
9.1. Normative References 9.1. Normative References
[I-D.ietf-uta-mta-sts]
Margolis, D., Risher, M., Ramakrishnan, B., Brotman, A.,
and J. Jones, "SMTP MTA Strict Transport Security (MTA-
STS)", draft-ietf-uta-mta-sts-19 (work in progress), May
2018.
[RFC1952] Deutsch, P., "GZIP file format specification version 4.3", [RFC1952] Deutsch, P., "GZIP file format specification version 4.3",
RFC 1952, DOI 10.17487/RFC1952, May 1996, RFC 1952, DOI 10.17487/RFC1952, May 1996,
<https://www.rfc-editor.org/info/rfc1952>. <https://www.rfc-editor.org/info/rfc1952>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997, <https://www.rfc- DOI 10.17487/RFC2119, March 1997,
editor.org/info/rfc2119>. <https://www.rfc-editor.org/info/rfc2119>.
[RFC3339] Klyne, G. and C. Newman, "Date and Time on the Internet: [RFC3339] Klyne, G. and C. Newman, "Date and Time on the Internet:
Timestamps", RFC 3339, DOI 10.17487/RFC3339, July 2002, Timestamps", RFC 3339, DOI 10.17487/RFC3339, July 2002,
<https://www.rfc-editor.org/info/rfc3339>. <https://www.rfc-editor.org/info/rfc3339>.
[RFC3492] Costello, A., "Punycode: A Bootstring encoding of Unicode [RFC3492] Costello, A., "Punycode: A Bootstring encoding of Unicode
for Internationalized Domain Names in Applications for Internationalized Domain Names in Applications
(IDNA)", RFC 3492, DOI 10.17487/RFC3492, March 2003, (IDNA)", RFC 3492, DOI 10.17487/RFC3492, March 2003,
<https://www.rfc-editor.org/info/rfc3492>. <https://www.rfc-editor.org/info/rfc3492>.
[RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform [RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
Resource Identifier (URI): Generic Syntax", STD 66, Resource Identifier (URI): Generic Syntax", STD 66,
RFC 3986, DOI 10.17487/RFC3986, January 2005, RFC 3986, DOI 10.17487/RFC3986, January 2005,
<https://www.rfc-editor.org/info/rfc3986>. <https://www.rfc-editor.org/info/rfc3986>.
[RFC4408] Wong, M. and W. Schlitt, "Sender Policy Framework (SPF)
for Authorizing Use of Domains in E-Mail, Version 1",
RFC 4408, DOI 10.17487/RFC4408, April 2006,
<https://www.rfc-editor.org/info/rfc4408>.
[RFC5234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax [RFC5234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", STD 68, RFC 5234, Specifications: ABNF", STD 68, RFC 5234,
DOI 10.17487/RFC5234, January 2008, <https://www.rfc- DOI 10.17487/RFC5234, January 2008,
editor.org/info/rfc5234>. <https://www.rfc-editor.org/info/rfc5234>.
[RFC5280] Cooper, D., Santesson, S., Farrell, S., Boeyen, S., [RFC5280] Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
Housley, R., and W. Polk, "Internet X.509 Public Key Housley, R., and W. Polk, "Internet X.509 Public Key
Infrastructure Certificate and Certificate Revocation List Infrastructure Certificate and Certificate Revocation List
(CRL) Profile", RFC 5280, DOI 10.17487/RFC5280, May 2008, (CRL) Profile", RFC 5280, DOI 10.17487/RFC5280, May 2008,
<https://www.rfc-editor.org/info/rfc5280>. <https://www.rfc-editor.org/info/rfc5280>.
[RFC5321] Klensin, J., "Simple Mail Transfer Protocol", RFC 5321, [RFC5321] Klensin, J., "Simple Mail Transfer Protocol", RFC 5321,
DOI 10.17487/RFC5321, October 2008, <https://www.rfc- DOI 10.17487/RFC5321, October 2008,
editor.org/info/rfc5321>. <https://www.rfc-editor.org/info/rfc5321>.
[RFC5322] Resnick, P., Ed., "Internet Message Format", RFC 5322, [RFC5322] Resnick, P., Ed., "Internet Message Format", RFC 5322,
DOI 10.17487/RFC5322, October 2008, <https://www.rfc- DOI 10.17487/RFC5322, October 2008,
editor.org/info/rfc5322>. <https://www.rfc-editor.org/info/rfc5322>.
[RFC5891] Klensin, J., "Internationalized Domain Names in [RFC5891] Klensin, J., "Internationalized Domain Names in
Applications (IDNA): Protocol", RFC 5891, Applications (IDNA): Protocol", RFC 5891,
DOI 10.17487/RFC5891, August 2010, <https://www.rfc- DOI 10.17487/RFC5891, August 2010,
editor.org/info/rfc5891>. <https://www.rfc-editor.org/info/rfc5891>.
[RFC5952] Kawamura, S. and M. Kawashima, "A Recommendation for IPv6 [RFC5952] Kawamura, S. and M. Kawashima, "A Recommendation for IPv6
Address Text Representation", RFC 5952, Address Text Representation", RFC 5952,
DOI 10.17487/RFC5952, August 2010, <https://www.rfc- DOI 10.17487/RFC5952, August 2010,
editor.org/info/rfc5952>. <https://www.rfc-editor.org/info/rfc5952>.
[RFC6068] Duerst, M., Masinter, L., and J. Zawinski, "The 'mailto' [RFC6068] Duerst, M., Masinter, L., and J. Zawinski, "The 'mailto'
URI Scheme", RFC 6068, DOI 10.17487/RFC6068, October 2010, URI Scheme", RFC 6068, DOI 10.17487/RFC6068, October 2010,
<https://www.rfc-editor.org/info/rfc6068>. <https://www.rfc-editor.org/info/rfc6068>.
[RFC6125] Saint-Andre, P. and J. Hodges, "Representation and
Verification of Domain-Based Application Service Identity
within Internet Public Key Infrastructure Using X.509
(PKIX) Certificates in the Context of Transport Layer
Security (TLS)", RFC 6125, DOI 10.17487/RFC6125, March
2011, <https://www.rfc-editor.org/info/rfc6125>.
[RFC6376] Crocker, D., Ed., Hansen, T., Ed., and M. Kucherawy, Ed., [RFC6376] Crocker, D., Ed., Hansen, T., Ed., and M. Kucherawy, Ed.,
"DomainKeys Identified Mail (DKIM) Signatures", STD 76, "DomainKeys Identified Mail (DKIM) Signatures", STD 76,
RFC 6376, DOI 10.17487/RFC6376, September 2011, RFC 6376, DOI 10.17487/RFC6376, September 2011,
<https://www.rfc-editor.org/info/rfc6376>. <https://www.rfc-editor.org/info/rfc6376>.
[RFC6522] Kucherawy, M., Ed., "The Multipart/Report Media Type for [RFC6522] Kucherawy, M., Ed., "The Multipart/Report Media Type for
the Reporting of Mail System Administrative Messages", the Reporting of Mail System Administrative Messages",
STD 73, RFC 6522, DOI 10.17487/RFC6522, January 2012, STD 73, RFC 6522, DOI 10.17487/RFC6522, January 2012,
<https://www.rfc-editor.org/info/rfc6522>. <https://www.rfc-editor.org/info/rfc6522>.
[RFC6698] Hoffman, P. and J. Schlyter, "The DNS-Based Authentication [RFC6698] Hoffman, P. and J. Schlyter, "The DNS-Based Authentication
of Named Entities (DANE) Transport Layer Security (TLS) of Named Entities (DANE) Transport Layer Security (TLS)
Protocol: TLSA", RFC 6698, DOI 10.17487/RFC6698, August Protocol: TLSA", RFC 6698, DOI 10.17487/RFC6698, August
2012, <https://www.rfc-editor.org/info/rfc6698>. 2012, <https://www.rfc-editor.org/info/rfc6698>.
[RFC6713] Levine, J., "The 'application/zlib' and 'application/gzip' [RFC6713] Levine, J., "The 'application/zlib' and 'application/gzip'
Media Types", RFC 6713, DOI 10.17487/RFC6713, August 2012, Media Types", RFC 6713, DOI 10.17487/RFC6713, August 2012,
<https://www.rfc-editor.org/info/rfc6713>. <https://www.rfc-editor.org/info/rfc6713>.
[RFC7208] Kitterman, S., "Sender Policy Framework (SPF) for
Authorizing Use of Domains in Email, Version 1", RFC 7208,
DOI 10.17487/RFC7208, April 2014,
<https://www.rfc-editor.org/info/rfc7208>.
[RFC7231] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer [RFC7231] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
Protocol (HTTP/1.1): Semantics and Content", RFC 7231, Protocol (HTTP/1.1): Semantics and Content", RFC 7231,
DOI 10.17487/RFC7231, June 2014, <https://www.rfc- DOI 10.17487/RFC7231, June 2014,
editor.org/info/rfc7231>. <https://www.rfc-editor.org/info/rfc7231>.
[RFC7405] Kyzivat, P., "Case-Sensitive String Support in ABNF", [RFC7405] Kyzivat, P., "Case-Sensitive String Support in ABNF",
RFC 7405, DOI 10.17487/RFC7405, December 2014, RFC 7405, DOI 10.17487/RFC7405, December 2014,
<https://www.rfc-editor.org/info/rfc7405>. <https://www.rfc-editor.org/info/rfc7405>.
[RFC7493] Bray, T., Ed., "The I-JSON Message Format", RFC 7493, [RFC7493] Bray, T., Ed., "The I-JSON Message Format", RFC 7493,
DOI 10.17487/RFC7493, March 2015, <https://www.rfc- DOI 10.17487/RFC7493, March 2015,
editor.org/info/rfc7493>. <https://www.rfc-editor.org/info/rfc7493>.
[RFC7671] Dukhovni, V. and W. Hardaker, "The DNS-Based
Authentication of Named Entities (DANE) Protocol: Updates
and Operational Guidance", RFC 7671, DOI 10.17487/RFC7671,
October 2015, <https://www.rfc-editor.org/info/rfc7671>.
[RFC7672] Dukhovni, V. and W. Hardaker, "SMTP Security via [RFC7672] Dukhovni, V. and W. Hardaker, "SMTP Security via
Opportunistic DNS-Based Authentication of Named Entities Opportunistic DNS-Based Authentication of Named Entities
(DANE) Transport Layer Security (TLS)", RFC 7672, (DANE) Transport Layer Security (TLS)", RFC 7672,
DOI 10.17487/RFC7672, October 2015, <https://www.rfc- DOI 10.17487/RFC7672, October 2015,
editor.org/info/rfc7672>. <https://www.rfc-editor.org/info/rfc7672>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>. May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[RFC8461] Margolis, D., Risher, M., Ramakrishnan, B., Brotman, A.,
and J. Jones, "SMTP MTA Strict Transport Security (MTA-
STS)", RFC 8461, DOI 10.17487/RFC8461, September 2018,
<https://www.rfc-editor.org/info/rfc8461>.
9.2. Informative References 9.2. Informative References
[RFC3207] Hoffman, P., "SMTP Service Extension for Secure SMTP over [RFC3207] Hoffman, P., "SMTP Service Extension for Secure SMTP over
Transport Layer Security", RFC 3207, DOI 10.17487/RFC3207, Transport Layer Security", RFC 3207, DOI 10.17487/RFC3207,
February 2002, <https://www.rfc-editor.org/info/rfc3207>. February 2002, <https://www.rfc-editor.org/info/rfc3207>.
[RFC3464] Moore, K. and G. Vaudreuil, "An Extensible Message Format [RFC3464] Moore, K. and G. Vaudreuil, "An Extensible Message Format
for Delivery Status Notifications", RFC 3464, for Delivery Status Notifications", RFC 3464,
DOI 10.17487/RFC3464, January 2003, <https://www.rfc- DOI 10.17487/RFC3464, January 2003,
editor.org/info/rfc3464>. <https://www.rfc-editor.org/info/rfc3464>.
[RFC3501] Crispin, M., "INTERNET MESSAGE ACCESS PROTOCOL - VERSION [RFC3501] Crispin, M., "INTERNET MESSAGE ACCESS PROTOCOL - VERSION
4rev1", RFC 3501, DOI 10.17487/RFC3501, March 2003, 4rev1", RFC 3501, DOI 10.17487/RFC3501, March 2003,
<https://www.rfc-editor.org/info/rfc3501>. <https://www.rfc-editor.org/info/rfc3501>.
[RFC3864] Klyne, G., Nottingham, M., and J. Mogul, "Registration [RFC3864] Klyne, G., Nottingham, M., and J. Mogul, "Registration
Procedures for Message Header Fields", BCP 90, RFC 3864, Procedures for Message Header Fields", BCP 90, RFC 3864,
DOI 10.17487/RFC3864, September 2004, <https://www.rfc- DOI 10.17487/RFC3864, September 2004,
editor.org/info/rfc3864>. <https://www.rfc-editor.org/info/rfc3864>.
[RFC6533] Hansen, T., Ed., Newman, C., and A. Melnikov, [RFC6533] Hansen, T., Ed., Newman, C., and A. Melnikov,
"Internationalized Delivery Status and Disposition "Internationalized Delivery Status and Disposition
Notifications", RFC 6533, DOI 10.17487/RFC6533, February Notifications", RFC 6533, DOI 10.17487/RFC6533, February
2012, <https://www.rfc-editor.org/info/rfc6533>. 2012, <https://www.rfc-editor.org/info/rfc6533>.
[RFC7321] McGrew, D. and P. Hoffman, "Cryptographic Algorithm
Implementation Requirements and Usage Guidance for
Encapsulating Security Payload (ESP) and Authentication
Header (AH)", RFC 7321, DOI 10.17487/RFC7321, August 2014,
<https://www.rfc-editor.org/info/rfc7321>.
[RFC7435] Dukhovni, V., "Opportunistic Security: Some Protection [RFC7435] Dukhovni, V., "Opportunistic Security: Some Protection
Most of the Time", RFC 7435, DOI 10.17487/RFC7435, Most of the Time", RFC 7435, DOI 10.17487/RFC7435,
December 2014, <https://www.rfc-editor.org/info/rfc7435>. December 2014, <https://www.rfc-editor.org/info/rfc7435>.
[RFC7469] Evans, C., Palmer, C., and R. Sleevi, "Public Key Pinning [RFC7469] Evans, C., Palmer, C., and R. Sleevi, "Public Key Pinning
Extension for HTTP", RFC 7469, DOI 10.17487/RFC7469, April Extension for HTTP", RFC 7469, DOI 10.17487/RFC7469, April
2015, <https://www.rfc-editor.org/info/rfc7469>. 2015, <https://www.rfc-editor.org/info/rfc7469>.
[RFC7489] Kucherawy, M., Ed. and E. Zwicky, Ed., "Domain-based [RFC7489] Kucherawy, M., Ed. and E. Zwicky, Ed., "Domain-based
Message Authentication, Reporting, and Conformance Message Authentication, Reporting, and Conformance
(DMARC)", RFC 7489, DOI 10.17487/RFC7489, March 2015, (DMARC)", RFC 7489, DOI 10.17487/RFC7489, March 2015,
<https://www.rfc-editor.org/info/rfc7489>. <https://www.rfc-editor.org/info/rfc7489>.
[RFC8098] Hansen, T., Ed. and A. Melnikov, Ed., "Message Disposition [RFC8098] Hansen, T., Ed. and A. Melnikov, Ed., "Message Disposition
Notification", STD 85, RFC 8098, DOI 10.17487/RFC8098, Notification", STD 85, RFC 8098, DOI 10.17487/RFC8098,
February 2017, <https://www.rfc-editor.org/info/rfc8098>. February 2017, <https://www.rfc-editor.org/info/rfc8098>.
9.3. URIs [RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for
Writing an IANA Considerations Section in RFCs", BCP 26,
[1] Section 2.2.3 RFC 8126, DOI 10.17487/RFC8126, June 2017,
<https://www.rfc-editor.org/info/rfc8126>.
[2] Section 3
Appendix A. Example Reporting Policy Appendix A. Example Reporting Policy
A.1. Report using MAILTO A.1. Report Using MAILTO
_smtp._tls.mail.example.com. IN TXT \ _smtp._tls.mail.example.com. IN TXT \
"v=TLSRPTv1;rua=mailto:reports@example.com" "v=TLSRPTv1;rua=mailto:reports@example.com"
A.2. Report using HTTPS A.2. Report Using HTTPS
_smtp._tls.mail.example.com. IN TXT \ _smtp._tls.mail.example.com. IN TXT \
"v=TLSRPTv1; \ "v=TLSRPTv1; \
rua=https://reporting.example.com/v1/tlsrpt" rua=https://reporting.example.com/v1/tlsrpt"
Appendix B. Example JSON Report Appendix B. Example JSON Report
Below is an example JSON report for messages from Company-X to Below is an example JSON report for messages from Company-X to
Company-Y, where 100 sessions were attempted to Company Y servers Company-Y, where 100 sessions were attempted to Company-Y servers
with an expired certificate and 200 sessions were attempted to with an expired certificate, and 200 sessions were attempted to
Company Y servers that did not successfully respond to the "STARTTLS" Company-Y servers that did not successfully respond to the "STARTTLS"
command. Additionally 3 sessions failed due to command. Additionally, 3 sessions failed due to
"X509_V_ERR_PROXY_PATH_LENGTH_EXCEEDED". "X509_V_ERR_PROXY_PATH_LENGTH_EXCEEDED".
{ {
"organization-name": "Company-X", "organization-name": "Company-X",
"date-range": { "date-range": {
"start-datetime": "2016-04-01T00:00:00Z", "start-datetime": "2016-04-01T00:00:00Z",
"end-datetime": "2016-04-01T23:59:59Z" "end-datetime": "2016-04-01T23:59:59Z"
}, },
"contact-info": "sts-reporting@company-x.example", "contact-info": "sts-reporting@company-x.example",
"report-id": "5065427c-23d3-47ca-b6e0-946ea0e8c4be", "report-id": "5065427c-23d3-47ca-b6e0-946ea0e8c4be",
skipping to change at page 31, line 44 skipping to change at page 33, line 17
"receiving-ip": "203.0.113.56", "receiving-ip": "203.0.113.56",
"failed-session-count": 200, "failed-session-count": 200,
"additional-information": "https://reports.company-x.example/ "additional-information": "https://reports.company-x.example/
report_info ? id = 5065427 c - 23 d3# StarttlsNotSupported " report_info ? id = 5065427 c - 23 d3# StarttlsNotSupported "
}, { }, {
"result-type": "validation-failure", "result-type": "validation-failure",
"sending-mta-ip": "198.51.100.62", "sending-mta-ip": "198.51.100.62",
"receiving-ip": "203.0.113.58", "receiving-ip": "203.0.113.58",
"receiving-mx-hostname": "mx-backup.mail.company-y.example", "receiving-mx-hostname": "mx-backup.mail.company-y.example",
"failed-session-count": 3, "failed-session-count": 3,
"failure-error-code": "X509_V_ERR_PROXY_PATH_LENGTH_EXCEEDED" "failure-reason-code": "X509_V_ERR_PROXY_PATH_LENGTH_EXCEEDED"
}] }]
}] }]
} }
Contributors
Laetitia Baudoin
Google, Inc.
lbaudoin@google.com
Authors' Addresses Authors' Addresses
Daniel Margolis Daniel Margolis
Google, Inc Google, Inc.
Email: dmargolis@google.com Email: dmargolis@google.com
Alexander Brotman Alexander Brotman
Comcast, Inc Comcast, Inc.
Email: alex_brotman@comcast.com Email: alex_brotman@comcast.com
Binu Ramakrishnan Binu Ramakrishnan
Yahoo!, Inc Oath, Inc.
Email: rbinu@oath.com Email: prbinu@yahoo.com
Janet Jones Janet Jones
Microsoft, Inc Microsoft, Inc.
Email: janet.jones@microsoft.com Email: janet.jones@microsoft.com
Mark Risher Mark Risher
Google, Inc Google, Inc.
Email: risher@google.com Email: risher@google.com
 End of changes. 198 change blocks. 
449 lines changed or deleted 466 lines changed or added

This html diff was produced by rfcdiff 1.47. The latest version is available from http://tools.ietf.org/tools/rfcdiff/